Because they are sloppy, that’s why. Because nobody thinks they are the greatest scientists in the world any more:
The UK Met Office has made a proposal for collation of station data, reported here by Foxnews , proposal here. Many, if not most, aspects of the proposal are obviously ones that have advocated here for a long time. Indeed, last summer, well before the Climategate Letters became public, I’d even suggested that the Met Office take over responsibility for this data set from CRU.
It’s a good suggestion. No one will ever trust the data that the CRU has “developed”. They refused to release it because they knew they had manipulated it so much it was unrecognizable.
If they expect to be taken seriously, all the data must be completely available, as well as the code they use to manipulate that data.